JPS59185792A - Method for forming highly corrosion resistant zinc-nickel alloy film - Google Patents

Abstract

PURPOSE:To form a zinc-nickel alloy film having excellent corrosion resistance, brightness and throwing power by performing plating in a plating bath contg. a specific concn. of respective ions of Zn, Ni and Cl and boric acid, and having a specific temp. CONSTITUTION:A plating bath contg. >=14g/l, more preferably 28-87g/l zinc chloride (anhydrous zinc chloride, etc.) in terms of concn. of zinc ion, >=12g/l, more preferably 37-62g/l nickel chloride (hexahydrated salt of nickel chloride, etc.) in terms of nickel ion, 0.2-1.5 nickel ion/zinc ion, 14g/l, more preferably 71-120g/l potassium chloride and/or sodium chloride in terms of chlorine ion concn. and about <=60g/l boric acid is kept at 10-50 deg.C and electrolysis is performed with such bath, by which a zinc-nickel alloy film is formed on a cathode.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming highly corrosion resistant zinc-nickel alloy coatings.

Conventionally, zinc plating has been widely used as a method of applying anti-corrosion surface treatment to steel substrates such as automotive electrical components.

However, due to salt damage problems in North America, Canada, etc., surface treatments with higher corrosion resistance have become necessary in recent years. For this reason, various types of highly corrosion-resistant surface treatments are being studied, and among these, zinc-nickel alloy plating is a very promising one.

For zinc-nickel valley gold plating, methods using a sulfuric acid bath, a sulfamic acid bath, a chloride bath using a large amount of ammonium chloride (hereinafter referred to as ammonium chloride bath), a birophosphoric acid bath, etc. have been known for a long time. However, these conventional methods have hardly been put into practical use due to defects in alloy composition stability, uniform electrodeposition, covering power, etc. In particular, pressed products such as electrical components for automobiles have uneven shapes, so it has been difficult to apply the above-described conventional methods to these pressed products. For example, sulfuric acid baths have recently been put into practical use as plating baths for steel plates, but this method has the disadvantage of poor covering power, so this method is particularly recommended when plating pressed products with uneven surfaces. It is extremely difficult to apply.

In order to solve the above problems, an ammonium chloride bath has recently been devised and announced. However, this method using a bath requires an organic brightener, making life management extremely difficult. In this case, it is already difficult to control the bath for alloy plating compared to plating of a single metal, and it is disadvantageous if the difficulty of bath control by such a brightening agent is compounded. This bath also contains a large amount of ammonium chloride as a conductive electrolyte. For this reason, it becomes difficult to sufficiently remove heavy metals in the treatment of this plating wastewater.

This is unfavorable in terms of environmental health, and requires a large amount of investment to fully remove it. From the above, there are major problems in implementing this method industrially.

Also known is a chloride bath (hereinafter referred to as chloride bath, to be distinguished from ammonium chloride bath) that uses a chloride consisting of potassium chloride or sodium chloride instead of ammonium chloride as a conductive electrolyte (U ,S,P142
85802). However, this known chloride bath
In nickel alloy plating, the nickel concentration in the bath is extremely low, so the nickel content in the film is 0.1.
It's as low as 5%. Therefore, it is difficult to say that the corrosion resistance of this alloy film is particularly excellent, that is, it has high corrosion resistance. The contents of the above-mentioned known prior art are based on the use of trace or small amounts of nickel in order to solve problems such as poor post-processability in a potassium chloride bath for galvanizing and deterioration in appearance due to eutectoidation of iron eluted from the work into the film. It seems that ions are added,
It seems that the purpose is not particularly to improve corrosion resistance. Furthermore, this chloride bath contains aromatic aldehyde as a brightening agent, aromatic acids such as benzoic acid and cinnamic acid, and nonionic surfactants as other additives. many. This is because a film with good gloss cannot be formed unless these brighteners are used.

Therefore, in this method using a chloride bath, as with the ammonium chloride bath mentioned above, bath control during alloy plating is extremely difficult, and as a result, quality stability is lacking, and furthermore, it is difficult to form a highly corrosion-resistant film. This is a problem because it cannot be done.

From the above, conventional zinc-nickel alloy plating using a sulfuric acid bath, etc., does not have good alloy composition stability, uniform electrodeposition, or covering power, and even when using the ammonium chloride bath or chloride bath mentioned above, It is difficult to manage,
Therefore, it lacks quality stability, and furthermore, it is not possible to simultaneously solve the problems of wastewater treatment (ammony chloride bath) and high corrosion resistance of the alloy film (chloride bath). Therefore, conventional methods have not been implemented industrially except in some cases, and it has been difficult to apply them to pressed products that have irregularities and require high corrosion resistance, gloss, and good appearance. .

Therefore, the present invention solves the above-mentioned problems all at once, and provides high corrosion resistance of the zinc-nickel alloy film, good gloss (even if no brightener is added), and stability of the alloy composition ( A method for forming a highly corrosion-resistant zinc-nickel alloy film that solves all of the following issues at once: stable quality), uniform electrodeposition, good covering power, ease of bath management, and elimination of difficulties in wastewater treatment. The purpose is to provide the following.

As a result of detailed studies on chloride baths, the present inventors have found that, unlike the conventional teachings of chloride baths, a tacky film with excellent corrosion resistance, gloss, and throwing power can be created with a bath composition with a high nickel ion concentration. The present invention was completed based on the discovery that the present invention can be obtained.

That is, the present invention provides a method for forming a zinc-nickel alloy film on a cathode by electrolyzing an aqueous solution of metal salts of zinc and nickel, in which the concentration of zinc chloride is 14 p/L or more as a zinc ion concentration, and the concentration of nickel The concentration of chloride is 12 as a nickel ion! II/L or more, the concentration of chloride consisting of at least one of potassium chloride and sodium chloride is 14 g/L or more as a chloride ion concentration, and the plating bath contains boric acid. It is characterized by a temperature of 10 to 50°C.

Zinc ions in the bath used in the method for forming highly corrosion resistant zinc-nickel alloy coatings are supplied as zinc chloride;
As for the chloride, anhydrous zinc chloride (ZnC12) is usually used, although the presence or absence of a hydrous salt and the degree of water content do not matter. The concentration is 14 p/L or more as a zinc ion concentration,
More preferably 28 to 87 p/L. If the zinc ion concentration is less than 14(]/L, the plating efficiency will deteriorate in terms of current efficiency and critical current density, which is practically undesirable.Also, although there is no particular limitation, if the concentration is more than 1100/L, zinc chloride In addition, the nickel ions in this bath are supplied as nickel chloride, and the presence or absence of a hydrated salt of the chloride, the degree of water content, and the oxidation number of nickel do not matter, but it is usually nickel chloride hexahydrate. Salt (N
iCl2.6H20) is used. Its concentration is 12 as a nickel ion concentration! :l/L or more, more preferably 37 to 62(]/L. If the concentration is as low as less than 12 g/L, the same disadvantages as in the case of zinc will occur and it is not practical.

Moreover, although there is no particular limitation, if it exceeds 861 J/L, it is economically unfavorable.

The weight concentration ratio of nickel ions and zinc ions (nickel ions/zinc ions) is preferably in the range of 0.2 to 1.5. If the concentration ratio is less than 0.2 and the bath temperature is 20 to 30°C, the coating nickel content will be less than 5% (see Figure 2), resulting in poor corrosion resistance and a powdery or matte coating. Only a thin film can be sewn, resulting in poor gloss (see Figure 3). If the concentration ratio is more than 1.5, the nickel content in the coating will be too high (20% or more) (see Figure 2), resulting in poor corrosion resistance and lower current density areas of the plated product. A black film forms and the appearance deteriorates (see Figure 3).

Potassium chloride, sodium chloride, or a mixture thereof is used as the conductive electrolyte in the bath used in the method of forming a highly corrosion-resistant zinc-nickel alloy coating. Its concentration is 1411/L or more in terms of chlorine ions, and more preferably 71 to 12C)o/L. Its concentration is 1. ,=4! If it is less than II/1, both the conductive effect and the good appearance of the film will be poor.

The upper limit of its concentration is not particularly limited, but 140
(]/L or more, the solubility of the salt becomes poor.

Boric acid is used as a bath component used in the method of forming a highly corrosion resistant zinc-nickel alloy film. The concentration of boric acid is not particularly limited, but is more preferably 5 to 30 p/L. Boric acid also acts as a pH buffering agent, but if boric acid is not added, the film will have poor gloss.
Moreover, the film becomes black in the parts of the plated product where the current density is low, which is not preferable. If the concentration exceeds 60(] /L, the solubility of boric acid deteriorates, which is not preferable.

The temperature of the bath used in the method of forming a highly corrosion resistant zinc-nickel alloy film is in the range of 10 to 50°C, more preferably 20 to 40°C. Bath temperature is 10℃
If it is less than that, it is not preferable because it impairs the solubility of various bath components and requires energy for cooling the bath. Moreover, if the bath temperature exceeds 50° C., the nickel content in the coating becomes too high and the corrosion resistance decreases, which is not preferable (see Fig. 2.3).

The pH of the plating bath is not particularly limited, but is preferably from 2.0 to 6.5, more preferably from 4.5 to 5.5. If the pH is less than 2.0, the dissolution of the zinc anode increases significantly and the bath composition tends to fluctuate, which is disadvantageous in terms of quality stability and in terms of uniform electrodeposition. Moreover, if PI-1 is more than 6.5, the solubility of zinc ions decreases, which is not preferable.

In addition, the bath components used in the method for forming highly corrosion-resistant zinc-nickel alloy coatings have good gloss, i.e., appearance, even if they do not contain any additives such as brighteners or contain only a small amount of bit inhibitors. It should be noted that good coatings are obtained. That is, the plating bath does not necessarily require the addition of a brightener such as an aromatic aldehyde, an aromatic acid, or a nonionic surfactant. It should be noted that this does not preclude the use of the above-mentioned brighteners in the bath components used in the method of forming highly corrosion-resistant zinc-nickel alloy films (although, if they are used, a film with even better gloss can be obtained).

The method of forming a highly corrosion-resistant zinc-nickel alloy film of the present invention is a chloride bath using at least one of potassium chloride and sodium chloride as a conductive electrolyte. According to the method of forming a highly corrosion-resistant zinc-nickel alloy film of the present invention, the nickel content in the film is in the range of 5 to 20% (see Figure 2.3). The coating within this range has extremely excellent corrosion resistance as shown in FIG. That is, zinc-
It is clear from the results of this example that a nickel alloy film shows high corrosion resistance when the nickel content in the film is in the range of 5 to 20%, and this fact can be confirmed from the following known materials. is also supported. That is, the value is 1
1 to 18% (USP 2.419.231), 8 to 15% (Japanese Unexamined Patent Publication No. 1983-152194), 10 to 1
6% (Proceedings of Inter
finish-80P, 128-132), 6.5
There is a report that it is between 9.5% and 9.5% (USP 3°420.754). (However, the plating bath in these cases is not a chloride bath using potassium chloride or the like.) Therefore, it is clear that known zinc-nickel alloy coatings with a nickel content in the range of 0.1 to 5% cannot be said to have sufficient corrosion resistance. That is, as mentioned above, this prior known technology uses a small amount or It seems that a small amount of nickel is added. Therefore, as with normal plating baths, a normal film cannot be obtained unless various brighteners are used, so it is explained that various brighteners are essential bath components. There is also a literature that says that when the nickel content is around 2%, especially when chromate treatment is applied, the corrosion resistance is equivalent to that of a galvanized film (l S [) ol Ilnikov ” E 1
electrodepositton of Z in
c −N 1ckel A 1loys ” 1y
Letal Finishing 1yjarc
h 1965P, 63-67), which further supports the above statement.

Furthermore, according to the method of forming a highly corrosion-resistant zinc-nickel alloy film of the present invention, even if the plating bath of the present invention does not contain any additives such as a brightening agent or contains only a small amount of a bit inhibitor, the brightness can be maintained. It is very good, and even if it is semi-gloss, a film with a good appearance can be obtained. In this respect, the method of forming the highly corrosion-resistant zinc-nickel alloy film of the present invention is a completely new plating method that has not been seen before. Therefore, according to the method of forming a highly corrosion-resistant zinc-nickel alloy film of the present invention, the control of the plating bath is extremely easy, and the quality of the film is not only good but also stable.

Therefore, the method of forming a highly corrosion-resistant zinc-nickel alloy film of the present invention is extremely advantageous in this respect compared to known chloride baths and ammonium chloride baths that contain brighteners as an essential component of the bath.

Furthermore, according to the method of forming a highly corrosion-resistant zinc-nickel alloy film of the present invention, there is very little variation in the nickel eutectoid rate due to changes in plating current density and changes in bath composition, as shown in Figures 1 and 2. A stable film is obtained.

Further, according to the method of forming a highly corrosion-resistant zinc-nickel alloy film of the present invention, uniform electrodeposition and covering power are also very superior to those of conventional bath-based methods. Therefore, this method is extremely advantageous for plating pressed products with irregularities such as automobile parts. In this respect, it can be said that it has become practical to form a highly corrosion-resistant zinc-nickel alloy film on pressed products such as automobile electrical components, which has not been practiced in the past. Furthermore, unlike known ammonium chloride baths, this method does not have any drawbacks in wastewater treatment, such as difficulty in removing harmful heavy metals. In particular, it is difficult to remove ammonium ions using a normal reverse osmosis membrane, so the method using an ammonium chloride bath has drawbacks when it comes to creating a closed system for a metsuki line, which is a goal in the future. This method does not have this drawback and is therefore very advantageous for closed system orientation.

From the above, the method for forming a highly corrosion-resistant zinc-nickel alloy film of the present invention provides high corrosion resistance, good gloss (good appearance), ease of managing the plating bath, stability of quality, uniform electrodeposition, and coating. This method is unique in that it is possible to form a zinc-nickel alloy film with excellent strength and strength, and there are no problems with wastewater treatment. Therefore, the present invention has made it possible to commercialize the plating of press-plated products with unevenness, such as automobile electrical components, which can sufficiently withstand salt damage.

The present invention will be explained below with reference to Examples.

Example 1 (1) The following two types of plating bath conditions (one is Example (A)
), others are comparative example (B)) test piece (SPCC
, 50 mm x 100 m + n, 0.8 t) with a cathode current density of 0.5.
μ plating was performed. The alloy composition in the film produced by this plating was analyzed by atomic absorption spectroscopy, and the results are shown in FIG. According to these results, the variation in the alloy composition due to the change in cathode current density, that is, the variation in the nickel content in the film, was 10 to 19% in the case of the example, and 11 to 41% in the case of the comparative example. It shows that there are very few compared to

(A) Plating bath conditions of the example: zinc chloride 140(]/L (zinc ion 67a/L), nickel chloride hexahydrate 200q/L, nickel ion 49q/L
L), potassium chloride 200g/L (chlorine ion 95p/L), potassium chloride 200g/L (chlorine ion 95p/
L), boric acid 10 (7/L.

Polyethylene glycol nonylphenyl ether 0:
01 (1/L (added as pit inhibitor), Pl-1
5.0, bath temperature 30°C, anode zinc plate (B) sulfuric acid bath conditions of comparative example zinc sulfate heptahydrate 130 p/i (zinc ion 30 (J/L)
), nickel ion 5 in nickel sulfate hexahydrate 250g/L
1/L), sodium sulfate 60i11/L (sulfate ion 48(]/L), sodium lauryl sulfate 0.1(]/
L (added as a bit inhibitor>, P) -12,5, bath temperature 50°C, anode zinc plate (2) The film of Example (A) above was subjected to electrolytic chromate treatment under the following conditions, and after this treatment The film was subjected to a salt spray test based on JIS Z2371.

According to the results, no red rust was observed in any of the test pieces even after 1000 hours, indicating extremely good corrosion resistance.

(C) Electrolytic chromate treatment conditions Chromium trioxide 25k/L, sulfuric acid 0.50/L.

Bath temperature 40 to 50°C, cathode current density 8A/dm2,
Processing time: 10 seconds, anode carbon plate (3), plating baths and conditions for Example (A> and Comparative Example (B)) in (1) above (total current 3A15)
As a result, a good glossy or semi-glossy film was obtained on the entire surface of the Hull Cell panel (total panel length: 100 m) in Example (A), whereas in Comparative Example (B), a coating of 4 cm on the high current side was obtained. Not only was it matte, but there was no plating over a 2.5 cm area on the low current side.

The table also shows the film thickness measurement results for each part of the Hull Cell panel. According to this, it was shown that the bath of Example (A>) had good uniform electrodeposition properties of the film.

According to the test results in (1), (2), and (3) above, Example (
The film formed by bath A) shows that the variation in the alloy composition of the film is small, and that it has high corrosion resistance, uniform electrodeposition, and good covering power.

Example 2 (1) The plating conditions such as the concentration of nickel chloride hexahydrate and the bath composition other than the bath temperature were set as follows, and the bath temperature '? Table 5 shows the concentration of nickel chloride hexahydrate at 30°C (film thickness unit: μ).
The same test piece as in Example (1) was plated with a film thickness of 4 μm by varying the nickel content within the range of /L), and the nickel content in the film was analyzed by atomic absorption spectroscopy to determine whether the nickel ions in the bath The influence of the weight concentration ratio of zinc ions on the alloy composition was investigated, and the results are shown in FIG.

According to this result, when plating is performed under the bath conditions of this example, a film with a stable alloy composition can be formed with a nickel content of 5.
．． 0 to 20%), indicating that it is extremely advantageous in terms of bath management.

Plating bath conditions Zinc chloride 120g/L (zinc ions 58g/L), potassium chloride 150g/L (chloride ions 71g/L), boric acid 5(]/L, PH5.0, cathode current density 4A/d
nu, anode zinc plate (2) The above Example 2 was prepared by changing the concentration of nickel chloride hexahydrate in the range of 10 to 300/L and 2.5 to 7.4 (1/L) of nickel ions at a bath temperature of 60°C. (
An experiment similar to 1) was conducted.

The results are also shown in Figure 2. This result shows that when the bath temperature is 60° C., the coating alloy composition changes greatly due to changes in the concentration ratio of both ions, which is disadvantageous in terms of bath management. Furthermore, the film obtained under the present plating bath conditions was matte and poor in appearance.

(3) Conditions other than the concentration of nickel chloride hexahydrate and the bath temperature were the same as the bath composition in Example 2 (1) above, the concentration ratio of both ions was in the range of 0.1 to 1.7, and the bath temperature was 10 The same test piece as in Example 1 (1) was plated with a film thickness of 4 μm at various temperatures in the range of 60° C. to 60° C. The appearance of these test pieces after plating was checked, and a salt spray test was conducted on the test pieces that had been subjected to the same electrolytic chromate treatment as in Example 1 (1). These results are shown in the 31st
Shown below. In addition, the nickel content in the film is added in FIG. 3 for some cases where the bath temperature is 30° C. and 60° C. In addition, "good corrosion resistance" in Fig. 3 means "good corrosion resistance".
The time until red rust appears in the test is 360 hours or more, and "poor corrosion resistance" means less than 360 hours. "Good appearance"
is a glossy or semi-glossy uniform film that has a "bad appearance"
This refers to the case where a powdery or matte film is deposited on the low concentration ratio side, or the case where a black film is deposited on the high concentration ratio side (low current density area). Further, the numbers in parentheses in FIG. 3 indicate the nickel content (%) in the alloy film.

According to the results, when corrosion resistance is good, the nickel content in the film is in the range of 5 to 20%, and when both high corrosion resistance and appearance are good, the concentration ratio of nickel ions and zinc ions is 0. 2 to 1.5, and the bath temperature is in the range of 10 to 50°C.

Furthermore, the corrosion resistance of the zinc film (thickness: 4 μm) that is formed when zinc alone is plated in a zincate bath after being treated in the same manner as above is almost the same as that of the nickel content of 2.5%. there were. That is, when the nickel content in the alloy film was 2.5%, no improvement in corrosion resistance was observed compared to when zinc was used alone.

In addition, when the corrosion resistance of each test piece was tested in the same manner as above at a bath temperature of 30°C without the above chromate treatment, it was found that when the nickel content in the alloy film was 2.5%, red rust occurred. The time until occurrence is 2
Only 4 hours, while in other cases it was 48 to 216 hours. That is, the corrosion resistance of the alloy film without chromate treatment was also good as in the case with chromate treatment, when the nickel content was in the range of 5 to 20%.

Example 3 Pipe (SPCC) with the following plating bath conditions.

When plating was carried out on a pipe having a length of 5Q mm, a diameter of 30 mm, and a diameter of 30 mm (O+-5t-), a good film with a glossy or single gloss was obtained over the entire surface of the pipe. The nickel content in the film was 16%.

Plating bath conditions Zinc chloride 70q/L (zinc ion 34(]/L), Nickel ion 45a in nickel chloride hexahydrate 180(]/L)
/L), sodium chloride 150f) / chlorine ion 91!11/L), boric acid 30! ;+/'L.

PH4.5, bath temperature 25℃, cathode current density 4A/dn+
2. Anode Zinc Plate Example 4 When the same pipe as in Example 3 was plated under the following plating bath conditions, a good semi-gloss film was obtained, and the nickel content in the film was 13%. .

Plating bath conditions Zinc chloride 50o/L (zinc ion 24g/L) Nickel chloride hexahydrate 70Q/L Nickel ion 17g/L
L, potassium chloride 30q/L (chlorine ion 14()
/L), boric acid 10g/L, P'H5,2, bath temperature 35
C, cathode current density 1 A/dm2, anode zinc plate Example 5 When a pipe similar to that of Example 3 was plated under the following plating bath conditions, only a matte and rough film was obtained. This result shows that a good film cannot be formed when the chlorine ion concentration is as low as 4.8 q/'L. Note that the nickel content in the film in this case was 11%.

Plating bath conditions: Zinc chloride 100o/L (zinc ion 48o/L)
, nickel chloride hexahydrate 150 (+ /L nickel ion 37!If/L), potassium chloride 10 (J/L (chlorine ion 4.8o'/L), boric acid 20 (1/L, 'PH
5.0, Bath temperature 30℃, cathode current density 4A/dm2, anode zinc plate comparative example Under bath conditions where the weight ratio of nickel ions/zinc ions is almost the same, the presence or absence of addition of boric acid was compared and studied below. .

Plating was performed on the same pipes as in Examples 4 and 5 above using a boric acid-free bath under the following plating bath conditions. The weight ratio of nickel ions/zinc ions was 0.73 under the following plating bath conditions, 0.71 in Example 4, and 0.71 in Example 5.
It was 0.77, which was almost the same in both cases. Under the following plating bath conditions, only a matte film was obtained, and a black film was deposited on the low current density portion of the inner surface of the pipe, and the film did not have good gloss. That is, it was found that addition of boric acid is necessary to improve the glossiness of the film. The nickel content in the film was 15%.

Plating bath conditions: Zinc chloride 140111/L (zinc ion 67g/L),
Nickel chloride hexahydrate 200 (]/L Nickel ion 49 (1/L), potassium chloride 200 g/L (chlorine ion 95 (1/L), PH 4.8, bath temperature 35°C, cathode current density 4 A/dm) , Regarding the composition of the plating bath from the anode zinc plate, the chloride power "lium or sodium chloride concentration is 1.4(]/L or more as a chlorine ion concentration,
The concentration of zinc chloride is 14Q /
The concentration of nickel chloride is 120/L or more as a nickel ion concentration, the weight concentration ratio of nickel ions and zinc ions is in the range of 0.2 to 1.5, and contains boric acid. When a zinc-nickel alloy film is formed under conditions in which the plating bath temperature is in the range of 10 to 50°C, that is, in the absence of organic brighteners, etc., the nickel concentration in the film is 10 to 50°C.
% to 20%, the film has high corrosion resistance, excellent gloss, and an extremely good appearance. In addition, the method for forming a highly corrosion-resistant zinc-nickel alloy film within the above range produces a high-quality film that is extremely stable against changes in cathode current density, nickel ion and zinc ion concentrations, etc., and is suitable for bath management. becomes extremely easy. In addition, this method has excellent uniform electrodeposition properties, so a film can be formed on the entire surface of the pipe.
Covering power is also good.

[Brief explanation of drawings]

Figure 1 shows the relationship between the cathode electrode density (A/dll12) and the nickel content (%) in the film, and Figure 2 shows the relationship between the weight concentration ratio of nickel ions and zinc ions and the plating bath temperature (°C) and the nickel content in the film. The relationship between the nickel content (%) and Figure 3 is a graph showing the relationship between the weight concentration ratio of nickel ions and zinc ions and the evaluation results of corrosion resistance and film appearance with respect to the plating bath temperature (°C). . Patent Applicant: Nippondenso Co., Ltd. Agent, Patent Attorney: Hirotoshi Okawa Patent Attorney: Shudo Fujitani Patent Attorney: Akio Maruyama
n'') Fig. 3 O... Corrosion resistance is good at first glance... Corrosion resistance and appearance are also Δ... Resistance 1 [Se 4 - Tato cage, good knee /) T Ruion and! Suzu Ion weight collapse (N17Zn”)

Claims (4)

[Claims] (1) In the method of electrolyzing an aqueous solution of metal salts of zinc and nickel to form a zinc-nickel alloy film on the cathode, the concentration of zinc chloride is 14 (1/L) as the zinc ion concentration.
(l) or more, the concentration of nickel chloride as nickel ions is 12 (] /L or more, and the concentration of chloride consisting of at least one of potassium chloride and sodium chloride is 14111 as chloride ions.
1. A method for forming a highly corrosion-resistant zinc-nickel alloy film, characterized in that the plating bath has a temperature of 10 to 50° C. and contains boric acid. (2) A highly corrosion-resistant zinc-nickel alloy according to claim 1, characterized in that the weight concentration ratio of nickel ions and zinc ions (nickel ions/zinc ions) is in the range of 0.2 to 1.5. Method of forming a film. (3) The method for forming a highly corrosion-resistant zinc-nickel alloy film according to claim 1, characterized in that the concentration of zinc chloride is in the range of 28 to 87(]/L as a zinc ion concentration. (4) The method for forming a highly corrosion-resistant zinc-nickel alloy film according to claim 1, characterized in that the concentration of nickel chloride is in the range of 37 to 62 g/L as a nickel ion concentration.